Pressure sensing device

ABSTRACT

Methods and apparatus for sensing pressure are disclosed. One disclosed pressure measuring device comprises a pressure transmission catheter including a stem portion and a sheath fixed to the stem portion. The disclosed sheath comprises a wall defining a cavity that is in fluid communication with a stem lumen defined by the stem portion. The disclosed sheath has a first transverse extent and a second transverse extent that is different from the first transverse extent.

FIELD OF THE INVENTION

The present invention relates to pressure sensing devices.

BACKGROUND OF THE INVENTION

Pressure measurement devices can be used to sense numerous internal bodypressures in humans and animals. Examples of pressures that may besensed include pulmonary pressure, venous pressure, left ventriclepressure, intracranial pressure, and bladder pressure. Thesemeasurements provide an important tool for medical research and clinicaldiagnosis. For example, hydrocephalus and head injuries can cause bodyfluids to build up within the brain. The resulting fluid pressurebuildup can result in death or serious brain damage. In another example,urinary dysfunction can cause fluid pressure to build up in the bladder.In a further example, intrapleural pressure measurements can be used tomonitor the respiration of infants who have been identified as being atrisk for sudden infant death syndrome.

Blood pressure measurements are particularly important for medicalresearch and diagnosis for a variety of reasons. Such measurementsprovide researchers with insight into the physiology and functioning ofthe heart. Blood pressure measurements also provide researchers withuseful information regarding the safety and efficacy of pharmaceuticalsand the toxicity of chemicals. By transducing blood pressure into asignal waveform, a variety of useful parameters can be extracted. Theseparameters provide valuable information for the diagnosis of heartdisease.

BRIEF SUMMARY OF THE INVENTION

The present disclosure relates generally to methods and apparatus forsensing pressure. One disclosed pressure measuring device comprises apressure transmission catheter including a stem portion and a sheathfixed to the stem portion. The disclosed sheath comprises a walldefining a cavity that is in fluid communication with a stem lumendefined by the stem portion. The disclosed sheath has a first transverseextent and a second transverse extent that is different from the firsttransverse extent.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective view showing a pressure measurement device 100in accordance with an exemplary embodiment of the present invention.

FIG. 2 is a perspective view of a distal portion 130 of the pressuretransmission catheter shown in the previous figure.

FIG. 3 is a cross-sectional view of the distal portion of the pressuretransmission catheter shown in the previous figure.

FIG. 4 is an additional cross-sectional view of the distal portion ofthe pressure transmission catheter shown in the previous figure.

FIG. 5 is an isometric view of the strut shown in the previous figure.

FIG. 6 is a side view of the strut shown in the previous figure.

FIG. 7 is a top view of the strut shown in the previous figure.

FIG. 8 is a partial cross sectional view of a pressure transmissioncatheter including a strut that is similar to the strut shown in theprevious figure.

FIG. 9 is a somewhat diagrammatic cross-sectional view of a pressuremeasurement device in accordance with an exemplary embodiment of thepresent invention.

FIG. 10 is an additional diagrammatic cross-sectional view of thepressure measurement device shown in the previous figure.

DETAILED DESCRIPTION OF THE INVENTION

The following detailed description should be read with reference to thedrawings in which similar elements in different drawings are numberedthe same. The drawings, which are not necessarily to scale, depictillustrative embodiments and are not intended to limit the scope of theinvention.

FIG. 1 is a perspective view showing a pressure measurement device 100in accordance with an exemplary embodiment of the present invention.Pressure measurement device 100 comprises an electronics housing 102 anda pressure transmission catheter 104. Pressure transmission catheter 104comprises a stem portion 106 and a sheath 108. Sheath 108 defines acavity 120 that is in fluid communication with a stem lumen 122 definedby stem portion 106.

In the embodiment of FIG. 1, sheath 108 comprises a first waist portion124, a second waist portion 126, and an intermediate portion 128 locatedbetween first waist portion 124 and second waist portion 126. Withreference to FIG. 1, it will be appreciated that first waist portion 124and second waist portion 126 of sheath 108 are both have a generallycylindrical shape. In FIG. 1, intermediate portion 128 of sheath 108 isshown generally having the geometry of a partially flattened tube.

FIG. 2 is a perspective view of a distal portion 130 of pressuretransmission catheter 104 shown in the previous figure. In theembodiment of FIG. 2, second waist portion 126 of sheath 108 is fixed tostem portion 106. First waist portion 124 of sheath 108 is coupled to astrut 134 by a seal 136. A distal portion 130 of strut 134 is visible inFIG. 2. With reference to FIG. 2, it will be appreciated that strut 134defines a strut lumen 138. In the embodiment of FIG. 2, the end of strutlumen 138 is sealed with a plug 140. In some embodiments of the presentinvention, strut 134 extends between the first waist portion and thesecond waist portion of the sheath. When this is the case, the strut mayprovide increased axial rigidity to the sheath.

With reference to FIG. 2, it will be appreciated that first waistportion 124 and second waist portion 126 of sheath 108 are both have agenerally cylindrical shape. In the embodiment of FIG. 2, anintermediate portion 128 is disposed between first waist portion 124 andsecond waist portion 126. In the embodiment of FIG. 2, intermediateportion 128 of sheath 108 has the geometry of a partially flattened tubeso that intermediate portion 128 has a first transverse extent 142 and asecond transverse extent 144 that is different from the first transverseextent 142. In the embodiment of FIG. 2, intermediate portion 128 ofsheath 108 has an axial extent 146. With reference to FIG. 2, it will beappreciated that axial extent 146 is greater than both first transverseextent 142 and second transverse extent 144.

Sheath 108 defines a cavity 120 that is in fluid communication with astem lumen 122 defined by stem portion 106. Also in the embodiment ofFIG. 2, intermediate portion 128 of sheath 108 has an outer surface 148having a surface area. In the embodiment of FIG. 2, the surface area ofouter surface 148 is greater than the lateral cross-sectional area ofstem lumen 122. This arrangement may to reduce the likelihood thatovergrowth will adversely affect the measuring capability of thepressure measurement device.

FIG. 3 is a cross-sectional view of distal portion 130 of pressuretransmission catheter 104 shown in the previous figure. In theembodiment of FIG. 3, second waist portion 126 of sheath 108 can be seendisposed about stem portion 106. In FIG. 3, strut 134 can be seendisposed in a cavity 120 defined by wall 150 of sheath 108. Withreference to FIG. 3, it will be appreciated that strut 134 comprises atubular member 152 defining a strut lumen 138. In the embodiment of FIG.3, strut lumen 138 fluidly communicates with a stem lumen 122 defined bystem portion 106.

With reference to FIG. 3, it will be appreciated that second waistportion 126 of sheath 108 has a generally circular shape. Withcontinuing reference to FIG. 3, it will be appreciated that intermediateportion 128 of sheath 108 has the geometry of a partially flattened tubeso that intermediate portion 128 has a first transverse extent 142 and asecond transverse extent 144 that is different from the first transverseextent 142. In the embodiment of FIG. 3, wall has a generally uniformwall thickness.

FIG. 4 is an additional cross-sectional view of distal portion 130 ofpressure transmission catheter 104 shown in the previous figure. In theembodiment of FIG. 4, intermediate portion 128 of sheath 108 comprises afirst major side 154, a second major side 156, a first minor side 158,and a second minor side 160. In FIG. 4, each side is shown having agenerally convex shape. In the embodiment of FIG. 4, each minor side hasgreater convexity than each major side. Also in the embodiment of FIG.4, each minor side has a first radius 162 and each major side has asecond radius 164 that is greater than first radius 162. In someapplications, the geometry illustrated in FIG. 4 provides a pressuresensing sheath in which each major side is more sensitive to pressurechanges than each minor side.

With reference to FIG. 4, it will be appreciated that strut 134comprises a tubular member 152 defining a strut lumen 138. Tubularmember 152 also defines a first cutout 166 and a second cutout 168. Inthe embodiment of FIG. 4, first major side 154 of sheath 108 extendsinto first cutout 166 defined by strut 134. Also in the embodiment ofFIG. 4, second major side 156 of sheath 108 extends into second cutout168 defined by strut 134.

Sheath 108 may comprise various metallic and non-metallic materialswithout deviating from the spirit and scope of the present invention.Examples of metallic materials that may be suitable in some applicationsinclude stainless steel, Elgiloy, MP-35N, titanium, gold, and platinum.

In some useful embodiments of the present invention, sheath 108comprises a resilient and/or reversibly deformable material. Forexample, sheath 108 may comprise an elastomeric material. The termelastomeric generally refers to a rubber-like material (e.g., a materialwhich can experience about a 5% deformation and return to the undeformedconfiguration). Examples of elastomeric materials include rubber (e.g.,natural rubber, silicone rubber, nitrile rubber, polysulfide rubber,etc.), thermoplastic elastomer (TPE), butyl, polyurethane, and neoprene.

Sheath 108 may comprise, for example, a thin walled silicone rubbertube. Silicone rubber that may be suitable in some applications iscommercially available from Dow Corning Corporation of Midland, Mich.which identifies this silicone rubber using the SILASTIC trademark.Alternatively, sheath 108 may comprise a thin walled silicone urethanecopolymer tube. Silicone urethane copolymers that may be suitable insome applications are commercially available from The Polymer TechnologyGroup of Berkeley, Calif. Sheath 108 may also comprise a thin walledpolycarbonate urethane. Polycarbonate urethanes that may be suitable insome applications are commercially available from The Polymer TechnologyGroup of Berkeley, Calif.

Stem portion 106 may comprise various metallic and non-metallicmaterials without deviating from the spirit and scope of the presentinvention. Examples of metallic materials that may be suitable in someapplications include stainless steel, Elgiloy, MP-35N, titanium, gold,and platinum. Examples of non-metallic materials that may be suitable insome applications include polycarbonate, polyurethane (PU), polyethylene(PE), polypropylene (PP), and polyvinylchloride (PVC),fluoropolytetrafluoroethylene (PTFE), and ePTFE.

FIG. 5 is an isometric view of strut 134 shown in the previous figure.Strut 134 comprises a tubular member 152 defining a strut lumen 138. Inthe embodiment of FIG. 5, tubular member 152 defines a first cutout 166that fluidly communicates with strut lumen 138.

FIG. 6 is a side view of strut 134 shown in the previous figure. Withreference to FIG. 6, it will be appreciated that tubular member 152 ofstrut 134 defines a first cutout 166 and a second cutout 168.

FIG. 7 is a top view of strut 134 shown in the previous figure. Withreference to FIG. 7, it will be appreciated a first cutout 166 definedby tubular member 152 fluidly communicates with strut lumen 138.

FIG. 8 is a partial cross sectional view of a pressure transmissioncatheter 204 including a strut 234 that is similar to the strut shown inthe previous figure. Pressure transmission catheter 204 comprises a stemportion 206 and a sheath 208. In the embodiment of FIG. 8, a proximalportion 232 of a strut 234 is fixed to stem portion 206 of pressuretransmission catheter 204. Sheath 208 defines a cavity 220 that is influid communication with a stem lumen 222 defined by stem portion 206.

In the embodiment of FIG. 8, sheath 208 comprises a first waist portion224, a second waist portion 226, and an intermediate portion 228 locatedbetween first waist portion 224 and second waist portion 226. In theembodiment of FIG. 8, second waist portion 226 of sheath 208 is fixed tostem portion 206. First waist portion 224 of sheath 208 is coupled tostrut 234 by a seal 236.

Strut 234 comprises a tubular member 252 defining a strut lumen 238. Inthe embodiment of FIG. 8, tubular member 252 defines a first cutout 266that fluidly communicates with strut lumen 238. Also in the embodimentof FIG. 8, tubular member 252 defines a second cutout 268 that fluidlycommunicates with strut lumen 238. In the embodiment of FIG. 8, a firstmajor side 254 of sheath 208 extends into first cutout 266 defined bystrut 234. Also in the embodiment of FIG. 8, a second major side 256 ofsheath 208 extends into second cutout 268 defined by strut 234.

FIG. 9 is a somewhat diagrammatic cross-sectional view of a pressuremeasurement device 300 in accordance with an exemplary embodiment of thepresent invention. Pressure measurement device 300 comprises a sensorhousing 370 and a pressure transmission catheter 304. Pressuretransmission catheter 304 comprises a stem portion 306 and a sheath 308.Stem portion 306 defines a stem lumen 322 that fluidly communicates withan interior 374 defined by sensor housing 370. A pressure sensor 372 isdisposed in interior 374 of sensor housing 370. Pressure sensor 372 maycomprise, for example, a piezo-resistive Wheatstone bridge siliconstrain gauge. Pressure sensors that may be suitable in some applicationsare commercially available from Sensonor of Horten, Norway.

In the embodiment of FIG. 9, a proximal portion 332 of a strut 334 isfixed to stem portion 306 of pressure transmission catheter 304. Adistal portion 330 of strut 334 is coupled to a first waist portion 324of a sheath 308 by a seal 336. With reference to FIG. 9, it will beappreciated that strut 334 defines a strut lumen 338 that fluidlycommunicates with stem lumen 322 defined by stem portion 306. A cutout366 defined by strut 334 is also visible in FIG. 9. Cutout 366 of isdisposed in fluid communication with strut lumen 338 and a cavity 320defined by sheath 308. In the embodiment of FIG. 9, the end of strutlumen 338 is sealed with a plug 340.

In the embodiment of FIG. 9, second waist portion 326 of sheath 308 isfixed to stem portion 306. With reference to FIG. 9, it will beappreciated that strut 334 extends between first waist portion 324 ofsheath 308 and a second waist portion 326 of sheath 308. Accordingly,strut 334 may provide increased axial rigidity to sheath 308.

FIG. 10 is an additional diagrammatic cross-sectional view of pressuremeasurement device 300 shown in the previous figure. In the embodimentof FIG. 10, a pressure transmitting fluid 376 is disposed in pressuremeasurement device 300 for transferring pressure between sheath 308 andpressure sensor 372. With reference to FIG. 10 it will be appreciatedthat pressure transmitting fluid 376 is disposed in cavity 320, strutlumen 338, stem lumen 322, and sensor housing interior 374.

Those skilled in the art will recognize that the present invention maybe manifested in a variety of forms other than the specific embodimentsdescribed herein. Accordingly, departures in form and detail may be madewithout departing from the spirit and scope of the present invention asdescribed in the appended claims. The entire disclosure of all patentsand patent applications mentioned in this document are herebyincorporated by reference herein.

1. An apparatus, comprising: a stem portion defining a lumen a sheathfixed to the stem portion; the sheath comprising a wall defining acavity that is in fluid communication with the lumen; the sheath havinga first transverse extent and a second transverse extent that isdifferent from the first transverse extent.
 2. The apparatus of claim 1,wherein an intermediate portion of the sheath has the geometry of apartially flattened tube.
 3. The apparatus of claim 1, wherein the wallhas a uniform wall thickness.
 4. The apparatus of claim 1, wherein thesheath comprises a first waist portion, a second waist portion, and anintermediate portion disposed therebetween.
 5. The apparatus of claim 4,wherein the intermediate portion of the sheath has an axial extent thatis greater than both the first transverse extent and the secondtransverse extent.
 6. The apparatus of claim 4, wherein: the lumen has alateral cross-sectional area; the intermediate portion of the sheath hasan outer surface having a surface area; the surface area of theintermediate portion is greater than the lateral cross-sectional area ofthe lumen, tending to reduce the likelihood that overgrowth willadversely effect the measuring capability of the apparatus.
 7. Theapparatus of claim 4, further comprising a strut extending between thefirst waist and the second waist for providing axial stability to thesheath.
 8. The apparatus of claim 4, wherein the intermediate portion ofthe sheath has a non-circular cross-sectional shape.
 9. The apparatus ofclaim 4, wherein the intermediate portion of the sheath has across-sectional shape defined by at least two different local radii ofcurvature.
 10. The apparatus of claim 4, wherein the intermediateportion of the sheath comprises a first major side, a second major side,a first minor side, and a second minor side.
 11. The apparatus of claim10, wherein each side has a generally convex shape.
 12. The apparatus ofclaim 10, further comprising a strut extending into the cavity; thestrut defining a first cutout and a second cutout; the first major sideextending into the first cutout; and the second major side extendinginto the second cutout.
 13. The apparatus of claim 10, wherein eachminor side has a first radius and each major side has a second radiusthat is greater than the first radius.
 14. The apparatus of claim 10,wherein each major side is more sensitive to pressure changes than eachminor side.
 15. The apparatus of claim 10, wherein each major side ismore compliant than each minor side.
 16. The apparatus of claim 10,wherein each major side offers less resistance to deflection than eachminor side.
 17. The apparatus of claim 10, wherein each minor side ismore rigid than each major side.
 18. The apparatus of claim 1, furthercomprising a pressure transmitting fluid disposed in the cavity definedby the wall of the sheath and a pressure sensor that contacts thepressure transmitting fluid.
 19. The apparatus of claim 1, wherein thewall of the sheath is substantially free of convolutions.
 20. Theapparatus of claim 1, further including a strut member extending betweena first waist and a second waist of the sheath.
 21. The apparatus ofclaim 1, wherein the wall of the sheath comprises an elastomericmaterial.
 22. The apparatus of claim 1, further comprising a pressuretransducer disposed in fluid communication with the lumen and a pressuretransmitting fluid disposed in the lumen for transferring pressurebetween the cavity and the pressure transducer; the pressure transducercomprising a housing defining an interior and a pressure sensor disposedin the interior.
 23. The apparatus of claim 1, wherein the stem portioncomprises a first material and the sheath comprises a second materialdifferent from the first material.
 24. The apparatus of claim 23,wherein the second material comprises an elastomeric material and thefirst material comprises a non-elastomeric material.
 25. The apparatusof claim 23, wherein the second material is more flexible than the firstmaterial.
 26. The apparatus of claim 23, wherein the first material hasa first modulus of elasticity and the second material has a secondmodulus of elasticity that is smaller than the first modulus ofelasticity.
 27. An apparatus, comprising: a stem portion defining alumen a sheath fixed to the stem portion; the sheath comprising a walldefining a cavity that is in fluid communication with the lumen; thesheath further comprising a first waist portion, a second waist portion,and an intermediate portion disposed therebetween. wherein anintermediate portion of the sheath has the geometry of a partiallyflattened tube.
 28. An apparatus, comprising: a stem portion defining alumen a sheath fixed to the stem portion; the sheath comprising a walldefining a cavity that is in fluid communication with the lumen; a strutthat extends into the cavity; the strut defining a first cutout; and afirst major side of the sheath extending into the first cutout.